The invention relates to combustion liner cap assemblies fitted to the upstream end of combustion liners in gas turbines and, specifically, to such liner cap assemblies formed by a casting process.
Conventional single nozzle combustor liner cap assemblies use louver cooling in the cone portion of the assembly to maintain the metal temperatures of the liner cap at acceptable levels. The louvers are punched through the metal of the liner cap, leaving cracks at the ends of the slots or holes, which can grow during normal operation of the gas turbine. In time, a crack from one louver may grow and combine with other cracks with the result that portions of the liner cap may break off and pass through the turbine, causing damage to the turbine nozzles and buckets. At the same time, the cap cowl (supporting the forward tip of the nozzle) is also subject to cracking in service, and even though the cap cowl is of a thicker material, large pieces have broken away, creating an even greater potential for substantial turbine damage.
The conventional single nozzle cap assemblies as described above are not repairable without disassembling the cap from the liner. The cost of repairs to cap assemblies are usually not justified and cracked cap assemblies are usually scrapped.
In one attempt to eliminate cracking of the louvered cone portion of a single nozzle combustion liner cap, a stacked ring concept was utilized, wherein the various rings were welded or brazed together.
In another attempt to solve the problem, the cap was constructed as an integral part of the liner, but nevertheless incorporated a stacked ring construction fabricated by welding and/or brazing.
The disadvantages of these constructions was not only the welding and/or brazing requirements, but also the fact that the cap assembly was constructed of numerous pieces, and extensive fixturing was required for proper assembly and maintenance.
The principal objective of this invention, therefore, is to provide a single nozzle cap assembly which overcomes the problems experienced with prior art liner cap assemblies, by constructing the cap assembly via, for example, an investment casting process. This not only eliminates the cracking problem, but also reduces the number of parts required to make the assembly. Other objectives of the invention are to efficiently utilize cooling air for cooling the liner cap; to simplify construction of the cap assembly to simplify repair procedures for damaged cap assemblies and to reduce cost of manufacturing cycle time of cap assemblies.
In accordance with one exemplary embodiment of the invention, a single nozzle combustion liner cap assembly is provided in the form of an outer annular sleeve connected to an inner center ring or cowl by an angled web or cone portion formed with multiple arrays of holes for introducing air through the cone portion where it is then diverted in desired directions by cooling slots formed by integral baffles or vanes formed on the downstream side of the cone portion. In one exemplary embodiment, three baffles or directional vanes are provided on the cone portion, the two innermost of which direct air radially inwardly along the downstream surface of the cone toward the cowl, and the third of which directs air in two opposite directions, i.e., inwardly and outwardly along the cone portion. In this exemplary embodiment, the entire cap assembly is formed as one piece by an otherwise conventional investment casting process which provides accurately dimensioned cooling apertures and associated flow directional vanes or baffles without danger of cracking as in the conventional louvered sheet metal cap liner assemblies.
It will be understood that the liner cap assembly may also be of two-piece construction where, for example, the outer sleeve portion is formed separately and is welded to the one piece cone/cowl portion.
It will be further understood that the cooling apertures themselves may be provided in the cone portion after casting by, for example, drilling.
Thus, in accordance with one embodiment of the invention there is provided a liner cap assembly for a combustion liner in a turbine comprising an outer tubular sleeve portion having upstream and downstream ends; an inner annular cowl having a central opening adapted to receive a forward end of a nozzle; and an inclined annular web or cone portion extending between the outer sleeve and the inner cowl, the cone portion extending rearwardly and radially inwardly from the downstream end of the outer sleeve to the inner cowl, the cone portion provided with a plurality of cooling apertures and a plurality of directional vanes or baffles on a downstream side of the cone portion adapted to divert air passing through the cooling apertures.
Additional objectives and advantages of the subject invention will become apparent from the detailed description which follows.